Communications networks are generally packet-switched networks that operate based on Internet Protocol (IP). Packets from a source device may travel to a destination device via paths chosen by forwarding devices connecting them. Since the forwarding devices operate independently and generally make local forwarding decisions, the path between the source and destination devices may not be the same for each packet, and may not be the same in each direction. This presents a challenge to trace packets and their paths through different forwarding devices in the network.